Wafer Laser Scanning for Uniform Modified Layer Depth
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Solution Overview
Problem
Existing wafer generation methods face issues with variations in modified layer formation depth, leading to increased machining allowances and separation failures, which reduce manufacturing efficiency.
Innovation Solution
A laser machining method involving multiple laser scans with changes in position to form linear irradiation trajectory lines orthogonal to the scanning direction, using intermittent irradiation with preceding and following laser beams to control the formation depth of modified layers and separation layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single laser scan is performed to form modified layers, then the process is simple and fast, but the depth variation of modified layers increases leading to separation failures
Solution Approach 1:
The single laser scan process is divided into multiple sequential scans. Each scan forms modified layers at different positions, and by controlling the overlap between consecutive scans, the depth variation is reduced. The modification layers from different scans overlap by a predetermined distance to ensure uniform depth across the entire workpiece surface.
Solution Approach 2:
Before performing the second and subsequent scans, the first scan establishes initial modified layers that serve as a foundation. The scanning conditions (speed, power, interval) are predetermined based on the material properties and desired modified layer characteristics, ensuring consistent depth formation across multiple scans.
2Manufacturing precision
If multiple laser scans are performed to reduce depth variation, then manufacturing precision improves, but the processing time increases
Solution Approach 1:
Instead of overlapping scans excessively (which would waste time), the invention uses a predetermined optimal overlap distance that is just sufficient to ensure depth uniformity. This partial overlap approach achieves the necessary precision without unnecessary time consumption.
Solution Approach 2:
The scanning parameters (speed, power, interval between scans, overlap distance) are optimized to achieve the desired modified layer depth uniformity in the minimum number of scans. By adjusting these parameters, the process balances precision requirements with time efficiency.
3Productivity
If the laser beam continuously irradiates the surface, then modified layers form quickly, but the depth control becomes difficult and variation increases
Solution Approach 1:
Instead of continuous irradiation, the laser beam performs periodic scanning with controlled intervals between scans. Each scan delivers energy in periodic pulses along the scanning direction, and the interval between consecutive scans is predetermined to allow heat dissipation and prevent excessive depth variation while maintaining formation speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces variation in modified layer depth, minimizing material loss and enhancing manufacturing efficiency by optimizing the formation of separation layers.
Implementation Method 1
irradiating a surface of a machining target with a laser beam
Implementation Method 2
a focal point of a laser beam having a wavelength to which a hexagonal monocrystal ingot is transparent
Data Source
AI summary
By performing a laser scan, which includes moving an irradiation position of a laser beam along a first direction while irradiating a surface of a machining target with the laser beam, for a plurality of times with changes in position within the surface in a second direction, a plurality of irradiation trajectory lines are formed along the second direction, the second direction being orthogonal to the first direction and defined along the surface, the irradiation trajectory lines being made of irradiation marks of the laser beam and linear along the first direction. In the single laser scan, the irradiation marks are formed at a plurality of irradiation positions by intermittently irradiating with a relative movement of the laser beam relative to the machining target along the first direction, and the irradiation marks formed by the irradiation with the laser beam that precedes are irradiated with the laser beam that follows.